1. Field of the Invention
The present invention relates to a resolver which detects the rotational position of a motor.
2. Description of the Related Art
In the past, a variable reluctance resolver (hereinafter, simply referred to as “resolver”), such as that disclosed in Japanese Patent Application Laid Open No. 2004-69374, has been proposed as a detection sensor which detects the rotational position of a rotating electrical machine such as an electric motor (i.e., a motor) or a generator. As shown in FIG. 10, a resolver 50 includes a resolver rotor (i.e., a rotor) 51 and a resolver stator (i.e., a stator) 52. The resolver rotor 51 is provided so as to rotate together with a drive shaft 53 that extends from a motor, not shown.
The resolver stator 52 is torus-shaped and surrounds the resolver rotor 51 from the outside. A plurality of teeth 54 are formed at equidistant intervals in the circumferential direction on the inner peripheral surface side of the resolver stator 52. Also, an exciting coil, a first output coil, and a second output coil, not shown, are wound around (the teeth 54 of) the resolver stator 52. The first output coil and the second output coil are such that the phases of the output signals (alternating current signals) detected by a control apparatus, not shown, are offset by 90 degrees.
When a reference signal (i.e., voltage) is output to the exciting coil of the resolver 50 in order to detect the rotational position of the motor, a gap width between the resolver rotor 51 and the resolver stator 52 changes such that the first output coil and second output coil each generate an output signal according to the gap width. The control apparatus then calculates the rotational position of a rotating portion (such as a rotor core) of the motor based on the output signals from the first output coil and second output coil, which correspond to the position of the resolver rotor 51.
The resolver 50 disclosed in Japanese Patent Application Laid Open No. 2004-69374 is arranged in a position close to the motor, i.e., resolver 50 is located adjacent to a portion (also referred to as the “coil end”) of the exciting coil of the motor, in order to make the entire motor, including the resolver 50, more compact. As a consequence of the proximity of the resolver 50 to the exciting coil, some of the magnetic flux generated by the exciting coil becomes noise to the resolver 50 when an exciting current is supplied to the exciting coil of the motor. Thus, noise (i.e., voltage) generated from the electromagnetic induction action of the noise resulting from this magnetism may ride on the output signals of the first output coil and the second output coil, and a reference signal sent to the exciting coil of the resolver stator 52. If this happens, the wave shape of the output signals may become distorted. As a result of this distortion, the rotational position of the rotating portion (i.e., the rotor core) of the motor may no longer be able to be accurately detected.
Also, an inverter, not shown, for supplying electric current to the motor and resolver 50 and the like, is provided near the resolver 50. In this case, noise (i.e., voltage) generated by the electromagnetic induction action resulting from the switching operation in the inverter may ride on the output signals and the reference signal. Therefore, in this case as well, noise generated from the electromagnetic induction action of the noise resulting from the magnetism generated by the inverter and the exciting coil of the motor and the like may ride on the output signals, thereby distorting the wave shapes of those signals. As a result, the rotational position of the rotating portion (i.e., the rotor core) of the motor is no longer able to be accurately detected, just as described above.